Place the 3 lb Yukon Gold potatoes cut into 3/4-inch chunks chunks in a large pot and cover with cold water by at least 1 inch. Add 1 tbsp of kosher salt for boiling water. Bring to a boil over high heat.

Once boiling, reduce heat to medium and cook until the 3 lb Yukon Gold potatoes cut into 3/4-inch chunks are just fork-tender — a fork should slide in easily but the chunks should still hold their shape, about 12–15 minutes. Do not overcook or they'll turn mushy when mixed.

Drain the 3 lb Yukon Gold potatoes cut into 3/4-inch chunks in a colander and spread them out on a baking sheet or leave in the colander to let steam escape for about 5 minutes. You want them dry, not wet. Let cool to room temperature, about 20–30 minutes.

While the 3 lb Yukon Gold potatoes cut into 3/4-inch chunks cool, whisk together the 1 cup mayonnaise, 2 tbsp yellow mustard, 3 tbsp sweet pickle relish, 1 tbsp apple cider vinegar, 1 tsp sugar, 1 tbsp kosher salt for boiling water, ¼ tsp black pepper freshly ground, and ¼ tsp celery salt in a large mixing bowl until smooth and well combined. Taste and adjust seasoning.

Add the cooled 3 lb Yukon Gold potatoes cut into 3/4-inch chunks chunks, chopped hard-boiled 4 eggs hard-boiled, diced stalks celery finely diced, 4 green onions thinly sliced, and ¼ cup red onion finely diced to the bowl with the dressing. Gently fold everything together with a large wooden spoon or spatula, being careful not to break up the 3 lb Yukon Gold potatoes cut into 3/4-inch chunks too much. You want creamy chunks, not mashed 3 lb Yukon Gold potatoes cut into 3/4-inch chunks.

Taste and adjust seasoning — it may need more 1 tbsp kosher salt for boiling water, a splash more 1 tbsp apple cider vinegar for tang, or a pinch more 1 tsp sugar. The flavor will mellow as it chills, so season slightly bolder than you think necessary.

Transfer the potato salad to a serving bowl. Smooth the top, sprinkle with 1 tsp paprika for garnish, and garnish with fresh fresh chives or 2 tbsp parsley if using. Cover tightly with plastic wrap and refrigerate for at least 1 hour before serving — 4 hours or overnight is even better.